1. Field of the Invention
The present invention relates generally to bicycle frame assemblies. In particular, the present invention relates to configurations for main frames including a head tube, a top tube and a down tube.
2. Description of the Related Art
Bicycles with frames fabricated from aluminum tubing have become increasingly popular. This can include tubes of standard and/or oversized tubing. Generally, the joints between the tubes of most aluminum bicycle frames are welded. An important junction in modern bicycle frames is the where the top tube, and the down tube meet up with the head tube. One reason for this is that the fork, which interfaces with the frame via a set of bearings known as a headset mounted in the head tube, acts as a long lever arm and can exert significant amounts of stress on the head tube. This stress can impact handling as well as the durability of the frame, as the top and/or down tubes may want to separate from the head tube because of the stresses experienced. The junction between the head tube and the top and down tubes can be particularly important in suspension bikes with large tires and/or stiff long-travel suspension forks which serve to increase the amount of stress experienced at the head tube. This is in addition to the stress experienced when absorbing bumps, and other rough trail conditions, which may be encountered while riding off-road.
Top tubes and down tubes have been getting bigger to achieve greater strength and rigidity. This has created problems in trying to accommodate the larger top and down tubes. The top and down tubes may be down sized at the head tube end to mate with a standard sized head tube. However, this reduces the effectiveness of the oversized tubing use for the top tube and down tube. An alternative approach has been to increase the diameter of the head tubes and the associated steer tube bore. While the larger diameter head tube avoids the need to crimp the top and down tube, the approach can require nonstandard bearings and a nonstandard steer tube. Significantly, this approach can add undesired weight, which is directly contrary to the desires of the market.